Water insoluble, nonvolatile, halogenated organic pollutants such as polychlorobiphenyls (PCB's), chlorinated pesticides, halogenated BNA's and the like are principle hazardous constituents at many Superfund sites and in many uncontrolled industrial waste sites. These pollutants are often found in soils and sediments and require detoxification as a result of government regulations or because of increasing environmental awareness of their high toxicity. At ambient temperature, most chlorinated pesticides and PCB's are in the solid phase, whereas halogenated BNA's are typically in the liquid phase. The solubilities of these compounds in water are low, even at elevated temperatures. Low solubilities result in great difficulties when attempting to decontaminate soils containing these troublesome compounds.
Effective detoxification of soils contaminated with toxic nonvolatile halogenated organics has prove to be an intractable and persistent problem in the past and pose major challenges to Superfund, industrial and other cleanup efforts. Available detoxification technologies are plagued with high treatment costs, rigorous reaction conditions, poor kinetics and low conversion efficiencies.
For example, incineration of contaminants in soil often produces acceptable detoxification efficiency for some nonvolatile halogenated organics, but requires a very high temperature to achieve 99.99+ percent conversion needed to decontaminate soils to environmentally acceptable levels. This occurs because the reaction equilibrium constants for halogens such as chlorine hydrogenation depend on reaction temperatures. At lower temperatures, equilibrium favors the reverse reaction shown as follows: ##STR1## K values at various temperatures for the above reaction can be tabulated as follows:
______________________________________ t (.sup..degree. F.) K Comment ______________________________________ 1,600 0.6 Reverse reaction favored 2,191 6.5 Forward reaction favored 2,800 14.0 Forward reaction heavily dominating ______________________________________
From the above Table it is evident that incineration temperatures of up to and over 2,800.degree. F. are required to achieve a very high K value, which translates into high conversion/destruction efficiency. However, maintaining such extremely high temperatures in available incinerator apparatus is cost prohibitive.
Other chemical detoxification technologies for soil treatment generally use corrosive and hazardous chemicals in rigorous reaction conditions and typically also required expensive organic solvents to solubilize the contaminants, thereby compounding the cleanup task. The hazards and wear and tear associated with these detoxification technologies are much higher, and generally the kinetics of conversion are slower, thereby severely reducing their practical application.